Method and apparatus for active temperature control of susceptors

ABSTRACT

A method and an apparatus utilized for thermal processing of substrates during semiconductor manufacturing. The method includes heating the substrate to a predetermined temperature using a heating assembly, cooling the substrate to the predetermined temperature using a cooling assembly located such that a thermal conductance region is provided between the heating and cooling assemblies, and adjusting a thermal conductance of the thermal conductance region to aid in heating and cooling of the substrate. The apparatus includes a heating assembly, a cooling assembly located such that a thermal conductance region is provided between the heating and cooling assemblies, and a structure or configuration for adjusting a thermal conductance of the thermal conductance region.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to co-pending application Ser. No.60/156,595, filed Sep. 29, 1999 and International Application No.PCT/US00/25503, filed Sep. 18, 2000. This application is related to andclaims priority to International Application No. PCT/US02/03403, filedon Feb. 25, 2002. The contents of those applications are incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to thermal processing ofsubstrates during semiconductor manufacturing.

2. Discussion of the Background

The increasing sophistication of semiconductor technology, and the neverending reduction in minimum line widths, is causing process engineers todemand increasing capabilities from the equipment used to manufacturesemiconductor integrated circuits. These requirements are leading inparticular to a need to minimize the cumulative thermal burden ofintegrated circuit processes. The thermal burden is the cumulativeamount of heat (in degree-minutes) absorbed by a wafer duringprocessing.

Sources of the thermal burden include diffusion furnaces, etch anddeposition processes, rapid thermal processing and annealing steps,among others. Typically, the temperature of a wafer rises during aprocess step to a steady state temperature, remains at that steady statetemperature for a predetermined amount of time, then drops back to roomtemperature. Each process step thus adds to the thermal burden of theoverall process. Though the peak temperature of a given process stepusually contributes the most to the incremental increase in the thermalburden, the need for processes requiring lower peak temperatures iscausing temperature ramp steps to contribute substantially to thethermal burden in an increasing number of cases. In some cases, there isessentially no steady state temperature. One key piece of equipment usedto control the temperature of a wafer during a process step is asusceptor. Each wafer is placed sequentially on a susceptor, and thetemperature of the wafer is controlled through the susceptor.

Minimizing the thermal burden in general, and precise wafer temperaturecontrol in particular, presents challenges to the manufacturers ofcapital equipment used to make integrated circuits. Those equipmentmanufacturers that can best meet the needs of the end users ofsemiconductor capital equipment stand to increase their market share.

SUMMARY OF THE INVENTION

The inventors of the present invention have identified important issuesand problems associated with wafer processing that are addressed by thepresent invention. For example, the inventors have determined that inorder to reduce the thermal burden on the semiconductor wafer duringprocessing it is advantageous to provide for rapid temperature controlof the wafer by heating and cooling in order to stabilize the wafer atone or more predetermined temperatures during processing. Simply heatingand cooling the wafer by controlling the temperature of a heat transfersolution and then circulating that solution through channels formed in awafer support structure will not provide optimal results. This methodsuffers from the amount of time and energy required to change the heattransfer solution from one temperature to another. The inventors havedetermined that what is needed is a way to allow both heating andcooling control of a wafer.

The diffusion of dopant atoms in a semiconductor structure is a processthat is exploited to produce desired device structures. Diffusion is athermodynamic process, so relatively high temperatures are used toachieve a desired profile in a reasonable time. However, the sameprofiles can be obtained at lower temperatures provided that suchtemperatures are maintained for longer periods of time. The cumulativeeffect of thermal processes during semiconductor integrated circuitmanufacturing steps can have the same effect as processes that utilizehigh temperatures. Unfortunately, the cumulative thermal burden of aprocess can cause excessive diffusion. Two contributing factors to thethermal burden of a process are the time required to heat a wafer andthe time required to cool the wafer. The inventors have identifiedadvantages in rapidly switching the temperature of a heat source so thata wafer temperature can be set to a desired temperature and changed to adifferent temperature during a single process.

The inventors have determined that the wafers need to be heated orcooled uniformly from a uniform initial temperature profile to a desiredtemperature. However, existing systems, such as flash lamp-basedheaters, inject more heat into the middle of the wafer than into theradial portions of the wafer, which results in non-uniform heating.Compounding this problem is the insulating effect of air around theperiphery of the wafer that impedes heat flow into and out of the wafer.Thus, the inventors have determined that what is needed is a way toprovide for a uniform thermal conductance.

The rate at which a heating or cooling structure can transfer heat intoor out of a wafer becomes important as soon as a change in thetemperature of a wafer is required. Existing systems rely on pureconductance, which is a function of the materials used to form thestructure. Alternative structures rely on conductance supplemented bycirculating heat exchange fluids. However, such systems are limited bythe capacity of the structure to transfer heat into and out of thefluid. Although such systems are capable of transferring huge quantitiesof heat, those systems do so with the assistance of large volumes ofheat exchanging equipment. In semiconductor manufacturing environments,space, and in particular floor space, is expensive, so there is anincentive to avoid bulky heating and cooling systems. Instead, attentionis focused on improving the performance of systems confined to existingspaces. The inventors have determined that what is needed is a way toenhance the thermal conductance of a heating or cooling structure.

The periphery of a wafer changes temperature at a different rate thandoes the bulk of the wafer. This difference can lead to an edge effectthat can adversely affect device performance. Accordingly, the inventorshave determined that what is needed is a way to spatially vary thethermal conductance of a structure used to heat or cool wafers.

The inventors have further determined that it is important to temporallyvary the thermal conductance of a structure used to heat or cool wafers.The inventors have determined that it is desirable to have a very highthermal conductance when the wafer is at a temperature significantlydifferent from the desired temperature so that one can transfer a lot ofheat into or out of a wafer so that the wafer reaches a desiredtemperature as quickly as possible. However, when the wafer is at orclose to a desired temperature, it is advantageous to have a low thermalconductance.

The presence of a temperature sensor (e.g., thermocouple) can provideaccurate measurements of the temperature at the sensory location. Insome instances, such sensors are used to determine whether a valveshould be opened or closed, thereby controlling the amount of coolantallowed to flow and the amount of energy being dissipated. However,thermocouples only provide temperature measurements at the location ofthe thermocouple. In addition, thermocouples break due to thermalcycling, and require electrical connections, including electricalinsulation, between the thermocouple and their associatedinstrumentation. Furthermore, in a system that provides for enhancedrates of heating and cooling, the adverse effects of thermal cycling areexacerbated. Accordingly, the inventors have determined that what isneeded is a way to sense the temperature so that the controller canadjust the valve and heater appropriately.

In an effort to address the important issues identified by the inventorsand discussed above, the inventors have constructed an apparatus andmethod as described in detail below. Accordingly, the present inventionadvantageously provides an apparatus and method for reducing thermalburden on a wafer during processing.

The present invention advantageously provides a method including thesteps of heating the wafer to a predetermined temperature when neededusing a heating assembly, cooling the wafer to the predeterminedtemperature when needed using a cooling assembly located such that athermal conductance region is provided between the heating assembly andthe cooling assembly, and adjusting a thermal conductance of the thermalconductance region to aid in heating and cooling of the wafer. Themethod preferably heats the wafer by utilizing an electrical resistiveelement attached to a heating body adapted to support the wafer, andpreferably cools the wafer by feeding a cooling fluid along a fluid pathwithin the cooling assembly.

A preferred embodiment of the method of the present invention adjuststhe thermal conductance of the thermal conductance region by providing abody within the thermal conductance region. The body includes a recessconfigured to define at least a portion of a chamber that receives aworking fluid. The pressure or density of working fluid present withinthe chamber can then be adjusted. The adjustment of the pressure ordensity of the working fluid present within the chamber preferablyincludes (1) evacuating the working fluid from the chamber during thestep of heating the wafer and (2) injecting the working fluid within thechamber during the step of cooling the wafer. Alternatively, the step ofadjusting the pressure or density of working fluid present within thechamber includes (1) injecting a first working fluid within the chamberduring the step of heating the wafer and (2) injecting a second workingfluid within the chamber during the step of cooling the wafer.

In one embodiment of the present invention, the body includes a recesswith a membrane therein. That membrane enables separate working fluidsto be provided and adjusts within each of the separate sections of thechamber. In another embodiment, the body includes a recess that has aside wall and a base. The side wall abuts the heating assembly such thatthe heating assembly, the side wall, and the base define the chamber.The base is spaced apart from the heating assembly by a gap distancethat varies over the base.

An alternate embodiment of the method of the present invention includesthe step of adjusting the thermal conductance of the thermal conductanceregion by adjusting a spatial relationship between the heating assemblyand the cooling assembly.

The present invention further advantageously provides a thermalprocessing apparatus including a heating assembly, a cooling assemblylocated such that a thermal conductance region is provided between theheating assembly and the cooling assembly, and a device configured toadjust a thermal conductance of the thermal conductance region. Theheating assembly preferably includes a heating body adapted to supportthe wafer and an electrical resistive element attached to the heatingbody. The cooling assembly preferably includes a cooling body, a fluidpath within the cooling body, and a feed device configured to feedcooling fluid along the fluid path.

A preferred embodiment of the apparatus of the present inventionincludes (1) a device with a body having a recess configured to defineat least a portion of a chamber configured to receive a working fluid,and (2) a fluid injection system configured to inject a working fluidwithin the chamber. The device preferably further includes a controlsystem configured to control the fluid injection system to achieve apredetermined density or a predetermined pressure of working fluidwithin the chamber. The device preferably further includes a pressureregulator, where the control system is configured to control thepressure regulator. The injection system preferably includes a gassupply configured to inject helium gas within the chamber as the workingfluid, and alternatively an additional gas supply configured to inject asecond gas within the chamber as the working fluid. The devicepreferably further includes a vacuum pump configured to evacuate thechamber.

The recess preferably has an aperture abutting the heating assembly todefine the chamber. The recess preferably has a platinum coating and amembrane therein defining separate sections within the chamber. Themembrane is in a form of a honeycomb, or alternatively in the form ofribs. The recess preferably has a side wall and a base, where the sidewall abuts the heating assembly such that the heating assembly, the sidewall, and the base define the chamber. The base is spaced apart from theheating assembly by a gap distance that varies over the base.

The preferred embodiment is also defined such that the heating assemblyand the cooling assembly are mounted on a pedestal having pluralconduits, the first conduit extending therethrough is configured toreceive power supply wires for the electrical resistive element. Thesecond conduit is configured to act as a supply line for the fluid path.The third conduit is configured to act as a discharge line for the fluidpath, and the fourth conduit is configured to act as a feed line for thechamber.

An alternate embodiment of the apparatus of the present invention isdefined such that the device includes a driving device configured toadjust a distance between the heating assembly and the cooling assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will become readily apparent with reference to thefollowing detailed description, particularly when considered inconjunction with the accompanying drawings, in which:

FIG. 1 is a schematic representation of a rapid thermal processingassembly according to an embodiment of the present invention;

FIG. 2 is a detailed representation of a rapid thermal processingassembly according to an embodiment of the present invention;

FIG. 3 is a cross-sectional view of an embodiment of a pedestal takenalong lines III-III in FIG. 2;

FIG. 4 is a cross-sectional view of an embodiment of a cooling assemblytaken along lines IV-IV in FIG. 2;

FIG. 5 is a plan view of a gap assembly according to an embodiment ofthe present invention;

FIG. 6 is a cross-sectional view of the gap assembly taken along linesVI-VI in FIG. 5;

FIG. 7 is a plan view of a gap assembly according to an alternativeembodiment of the present invention;

FIG. 8 is a cross-sectional view of the gap assembly taken along linesVIII-VIII in FIG. 7;

FIG. 9 is a flow diagram of a method of operation according to anembodiment of the present invention; and

FIG. 10 is a flow diagram of a method of operation according to analternative embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described with reference to preferredembodiments illustrated in the figures. The present invention generallyrelates to a method and an apparatus for actively controlling thetemperature of a susceptor. The apparatus supports a wafer with aheating assembly, beneath which is a thermal conductance region whosethermal conductance is regulated. Furthermore, a cooling assembly isprovided beneath the thermal conductance region. The present inventionfurther includes several methods of operating the apparatus.

Referring now to the drawings, FIG. 1 is an overview of a preferredembodiment of a rapid thermal processing assembly or apparatus 100,which acts essentially as, for example, a novel thermal switch forheating and cooling susceptors used for processing semiconductor wafers.The apparatus 100 generally includes a heating assembly 102, a coolingassembly 106, and a gap assembly or device 104 provided within a thermalconductance region between the heating assembly 102 and the coolingassembly 106. The gap assembly 104 is configured to adjust a thermalconductance of the thermal conductance region, as will be described infurther detail below. A substrate 108 (e.g., a semiconductor wafer or anLCD panel) is placed on top of the uppermost surface of the processingassembly 100. More generally, the substrate is a workpiece (1) with onesurface that is substantially flat, and (2) that is preferably the samesize or smaller than the processing assembly 100.

The heating assembly 102 is used to increase the temperature of thesubstrate 108 to a desired temperature, for example, duringinitialization of the manufacturing process in order to preheat thesubstrate 108 for processing. The cooling assembly 106 is used to lowerthe temperature of substrate 108 as desired during the manufacturingprocess. The heating assembly 102 and the cooling assembly 106 allow thetemperature level to be increased or decreased as required during themanufacturing process. The gap assembly 104 is substantially alignedwith and may either be fixedly or separately connected to the coolingassembly 106. The uppermost surface may be a heating assembly 102 asshown in FIG. 1, or the order of the heating assembly 106 may beswitched such that the cooling assembly 106 is the uppermost surface.When, for example, one is utilizing the assembly 100 for a “spike”anneal (i.e., rapid heat-up to a temperature and rapid cool-down), it ispreferable to have the heating element located proximate the substrate.One reason for such a design is that the heating element can befabricated with less thermal inertia than the cooling element.Furthermore, the primary cooling mechanism at the elevated temperaturesis, at least initially, radiative transport (this provides some time tocompensate for the cooling element thermal lag).

Additional elements, described in detail below, serve to change thethermal conductance of gap assembly 104 as needed to ensure that thesubstrate 108 changes rapidly in temperature to a desired predeterminedtemperature. Note that the location of the gap assembly 104 in betweenthe heating assembly 102 and the cooling assembly 106 allows the gapassembly 104 to either insulate the substrate 108 from the coolingassembly 106, or facilitate thermal transfer from the cooling assembly106 to the substrate 108. Similarly, the gap assembly 104 can eitherinsulate the substrate 108 from the heating assembly 102, or facilitatethermal transfer from the heating assembly 102 to the substrate 108.

The heating assembly 102 is connectable to the gap assembly 104. The gapassembly 104 is connectable to the cooling assembly 106. The substrate108 is removably connected to the heating assembly 102, for example, bya chuck assembly such as an electrostatic chuck manufactured by TokyoElectron Limited, or the one disclosed in U.S. Pat. No. 5,310,453entitled “Plasma process method using an electrostatic chuck” andassigned to Tokyo Electron Yamanashi Limited (Fukasawa et al.). Inoperation, the heating assembly 102 is used to raise the temperature ofsubstrate 108 to a desired temperature, and the cooling assembly 106 isused to reduce the temperature of substrate 108 to a desiredtemperature. However, the effectiveness of the cooling assembly 106 tocontrol the temperature of the substrate 108 depends on the thermalconductivity of the gap assembly 104, due to the presence of the gapassembly 104 in between the substrate 108 and the cooling assembly 106.Therefore, to enhance the rate at which the substrate 108 can be heated,the gap assembly 104 is adjusted to reduce the rate of heat transferacross the gap assembly 104 (i.e., lower the thermal conductivity of thegap assembly 104). Likewise, when rapid cooling of the substrate 108 isrequired, the thermal conductance of gap assembly 104 is adjusted toenhance the rate of heat transfer across the gap assembly 104 (i.e., thethermal conductivity of the gap assembly 104 is increased).

FIG. 2 is a detailed view of the rapid thermal processing assembly orapparatus 100. The apparatus 100 preferably includes a heating assembly102, a gap assembly or device 104, a cooling assembly 106, a helium gassupply 136, a first valve 128, a second valve 130, a vacuum pump 126, apressure regulator 134, a cooling channel feed 120, a cooling channelreturn 122, a pedestal 118, a vacuum feed 138, a first vacuum line 124,a gas line 132, a controller 156, an electrical wire feed through 114, asecond vacuum line 125, a membrane 113, heater wires 194, and a powersupply 157. The interrelationship of the elements of the apparatus 100is depicted in FIG. 2, and is explained in detail below.

The heating assembly 102 includes a heating body 196 and at least oneelectrical resistive element 110 attached to the heating body 196, forexample, by embedding the elements 110 within the body 196. The heatingbody 196 is preferably formed from quartz, although the body 196 canalternatively be made from materials, such as sapphire and alumina, oraluminum as in the electrostatic chuck manufactured by Tokyo ElectronLimited, or the one disclosed in U.S. Pat. No. 5,310,453 entitled“Plasma process method using an electrostatic chuck” and assigned toTokyo Electron Yamanashi Limited (Fukasawa et al.). Still alternatively,the heating body may be formed of carbon, silicon carbide, siliconnitride, or any other material known to be used for forming a heatingassembly. It is to be understood that any one or more of these knownmaterials for forming a heating assembly may be used in combination withthe present invention without deviating from the spirit and scope of thepresent invention.

The electrical resistive element 110 is preferably made of Kanthal™,although alternatively the element 110 can be made of materials such asNikrothal, tungsten, etc. The advantage of using Kanthal™ to form theelectrical resistive element 10 is its high resistivity. However, thecoefficient of thermal expansion of Kanthal™ is an order of magnitudelarger than that of quartz, which means that the heating assembly shouldbe made to include space for the Kanthal™ to expand within the quartzenclosure. For further details, an exemplary design and fabrication ofthe heating assembly 102 is described in International Application No.PCT/US00/25503 filed on Sep. 28, 2000 (based upon U.S. Ser. No.60/156,595).

The controller 156 preferably includes a microprocessor, such as aPentium® processor, memory for data and process recipe storage, and adata bus for transferring data to and from the memory. The controller156 is electrically connected to and configured to control the operationof the vacuum pump 126, the first valve 128, the second valve 130, thepressure regulator 134, the power supply 157, and the coolant fluidsupply and pump 173. Such electrical connections will be readilyapparent to one of ordinary skill in the art.

With reference to FIG. 3, the pedestal 118 is preferably made of quartzor other similar material, for example alumina or sapphire. The pedestal118 has a lower first end, and an upper second end. The second end ispositioned opposite to the first end and is connected to the coolingassembly 106. The pedestal 118 is preferably cylindrical in shape,although other shapes can alternatively be utilized. The cooling channelfeed 120 and cooling channel return 122 are formed within the pedestal118, for example, by milling through-passages from the first end ofpedestal 118 to the second end of pedestal 118 along axes parallel to,but displaced from, a principal or central axis of the cylindricalpedestal. The cooling channel feed 120 and cooling channel return 122are formed so that the cooling channel feed 120 and the cooling channelreturn 122 are arranged on opposite sides of the principle axis of thepedestal 118, with gas feed line 116 positioned therebetween. The gasfeed line 116 extends coaxially with the principle axis of the pedestal118. The diameter of pedestal 118 is sufficiently large such that thecooling channel feed 120, the cooling channel return 122, and the gasfeed line 116 can be formed therein without compromising the structuralintegrity of pedestal 118, and without overlapping.

The vacuum feed 138 is provided within the gas feed line 116, which isformed in the pedestal 118, for example, by standard milling methods,and includes a lower first end and an upper second end. The lower firstend of the vacuum feed 138 is fixedly attached to a sealing cap toensure that neither gas nor vacuum can escape from vacuum feed 138. Thesecond end of vacuum feed 138 is open, and exposed to gap recess 111(see FIG. 2). The vacuum feed 138 is formed along the principal axis ofthe pedestal 118.

As depicted in FIG. 2, the electrical wire feed through 114 is fixedlyattached to the conduit 142, which is a hollow cylinder passing throughthe length of the vacuum feed 138, and along the principal axis of thepedestal 118. The wire feed through 114 forms a vacuum seal with thevacuum feed 138 so that there is no leak. The electrical wire feedthrough 114 passes through the lower first end of vacuum feed 138. Theconduit 142 is parallel to and coincident to the principal axis of thepedestal 118, and is sufficiently large that electrical connections toresistive elements 110 pass freely through the conduit 142.

With reference to FIGS. 2 and 4, the cooling assembly 106 is fixedlyattached to the pedestal 118, and includes a cooling body 107 and acoolant channel or fluid path 112. The cooling assembly 106 ispreferably made out of the same materials as the pedestal 118, althoughother similar materials can alternatively be utilized. For example, thecooling assembly 106 may be made from materials, such as sapphire andalumina, aluminum, carbon, silicon carbide, silicon nitride, or anyother material known to be used for forming a cooling assembly. It is tobe understood that any one or more of these known materials for forminga cooling assembly may be used in combination with the present inventionwithout deviating from the spirit and scope of the present invention.

The coolant channel 112 preferably follows a serpentine path designed toallow uniform cooling across an upper surface of the cooling assembly106 to which gap assembly 104 is attached. Alternative coolant channel112 configurations will be readily apparent to one of ordinary skill inthe art. The coolant channel 112 has a first end fluidly connected tothe cooling channel feed 120, and a second end fluidly connected to thecooling channel return 122.

FIG. 4 is a cross-sectional view along lines IV-IV in FIG. 2 thatdepicts the coolant channel 112, the cooling channel return 122, thecooling channel feed 120, conduit 142, and the vacuum feed 138. Thecoolant channel 112 is formed in the cooling body 107 using standardtechniques and is configured to provide a fluid path for cooling fluidtraveling therethrough.

With reference to FIGS. 2, 5 and 6, the gap assembly or device 104occupying a thermal conductance region includes a gap body 184 with agap recess 111. The gap assembly 104 is preferably made out of the samematerials as the pedestal 118, although other similar materials canalternatively be used. FIG. 5 is a plan view of the gap assembly 104that includes the gap body 184, the vacuum feed 138, and the conduit142. The gap recess 111 and the lower surface of the heating body 196define a chamber configured to receive a working fluid as described indetail below. For convenience of construction, the gap body 184, thevacuum feed 138 and the conduit 142 are preferably cylindrical incross-section, and are coaxially aligned, although other shapes andconfigurations can alternatively be utilized.

FIG. 6 is a cross-sectional view along lines VI-VI in FIG. 5 of the gapassembly 104, which depicts an optional metal such as, for example,platinum, coating 115, a floor or base 127, the gap recess 111, thevacuum feed 138, and the conduit 142. The interrelation of theseelements is depicted in FIG. 6, and described in detail below. Theoptional metal coating 115 is formed, for example, by sputter depositinga layer approximately 1 μm thick onto the floor 127 of gap body 184. Thegap body 184 is preferably formed of quartz or other materials withcomparable material properties.

Preferably, a membrane 113 is positioned within the recess 111. Themembrane 113 is preferably formed from a quartz honeycomb or evensparsely distributed quartz ribs (see the honeycomb walls/ribs 113A,113B, 113C, and 113D depicted in FIG. 6) machined into a thick piece ofquartz, where the quartz honeycomb or ribs are bonded to a bottomsurface of the heating assembly 102 and bonded to the floor 127 of therecess 111 prior to deposition of platinum coating 115 or insertion of aplatinum sheet. Due to the viscous nature of the quartz bonding frit,the honeycomb or ribs can be “dipped” into a thin layer of the frit.Thereafter, the solvents can be baked out, the quartz pieces assembled,and the assembled product bonded in a high temperature kiln. The quartzhoneycomb or ribs aid in distributing a load applied to a backside of athin, large diameter quartz heating assembly 102 when the gap issubjected to atmospheric pressure gas (or greater) and an environmentexternal to the processing assembly that is in a vacuum. Conversely, thehoneycomb or ribs can be used to support a compressive load when the gapis evacuated and the external ambient environment is at atmosphericpressure.

Referring again to FIG. 2, the power supply 157 provides electricalpower to the electrical resistive element 110 via heater wires 194. Thepower supply 157 thus needs to be able to provide sufficient power, forexample power up to 25 kW. The power supply 157 is calibratedexperimentally with respect to the electrical resistive element 110 sothat any given power output (i.e., current and voltage setting)corresponds to a known thermal output by the electrical resistiveelement 110, thereby determining the temperature to which the substrate108 will be heated by the electrical resistive element 110.Alternatively, the power supply 157 is calibrated using a pyrometer. Bycontrolling the temperature based upon a given power output whichprovides a known thermal output, the present invention has eliminatedthe need for the use of a thermocouple to detect the temperature of thesubstrate 108. However, alternatively a temperature sensor could beutilized with the present invention if so desired to precisely measurethe temperature level of the substrate 108. Temperature sensors mayinclude a pyrometer located in the structure opposite the substrate(e.g. “viewing” the substrate from above) such as those commerciallyavailable through Sekidenko (Model 2000 optical fiber thermometer), anemissometer such as those commercially available from Sekidenko (Model2100 emissometer), or band-edge temperature measurement such as thatdescribed in pending U.S. application 60/174,593 and 60/189,043. Thelatter device requires optically coupling, via fiber optics, broadbandIR radiation to the backside of the substrate and on a substrate sideopposite the illumination monitoring the movement (as a function oftemperature) of the transmission band-edge. An additional well-knowntechnique to monitor the temperature of the heating element includesmeasuring the element resistance from the known voltage across theelement and the current, and computing the temperature from its knownresistivity-temperature dependence. This approach is most useful whenthe heating element material has a large temperature coefficient forresistivity.

With reference again to FIG. 2, the thermal processing assembly 100advantageously provides an apparatus that can efficiently heat a waferduring processing or prior to commencement of processing if so desired,for example, in order to preheat a wafer to an optimal temperature priorto or during processing. In operation, with the substrate 108 on theheating assembly 102 of the rapid thermal processing assembly 100, acommand from the controller 156 causes the second valve 130 to be set tovacuum pump, hence closing off line 132, and the first valve 128 to beopened. As a result, any residual gas in the gas feed through 116 and inthe gap recess 111 is pumped out. The controller 156 sends a signal topower supply 157 to apply electrical power, at a level corresponding toa desired temperature setting, to the electrical resistive element 110via heater wires 194.

When a reduction in wafer temperature is desired, the second valve 130is opened to the gas supply 136 (i.e., second valve 130 is closed tovacuum pump 126) while the first valve 128 to the vacuum pump is closed,and the pressure regulator 134 is set to allow a given amount of working“fluid” (e.g., helium or other similar conductor in either a gaseous orliquid state) to flow through gas line 132 to vacuum line 125, throughgas feed through 116, and to gap recess 111. The pressure regulator 134sets the gas pressure within gap recess 111. The result of the workingfluid within the gap recess 111 is a dramatic increase in the thermalconductance of gap assembly 104. Simultaneously, cooling fluid of apredetermined temperature is pumped into cooling channel feed 120,through coolant channel 112 to cool the substrate 108 to thepredetermined temperature, and back to the cooler through coolingchannel return 122. Even during heating operations, coolant may bepumped through the coolant channels since the heater is thermally(conductively) insulated from the cooler via the gap assembly 104 in avacuum state. Thus, the simultaneous action of flooding the evacuatedgap recess 111 with gas from a helium gas supply 136, along with pumpingcooling fluid through coolant channel 112 (and turning off the powerapplied to electrical resistive elements 110) causes the apparatus toact as a heat switch. Since the height of gap recess 111 is small, thevolume associated with the gap recess 111 is also small. Consequently,reversing the above process also causes the apparatus of the presentinvention to act as a heat switch. Thus, the present invention serves asa bi-directional heat switch.

In an alternate configuration, helium gas supply 136 and pressureregulator 134 are replaced by plural working fluid sources and apressure regulator for each working fluid source. In operation with thisconfiguration and upon command from controller 156, one working fluid isturned off and another working fluid is turned on. As a result, theworking fluid in gap recess 111 changes from one working with oneconductance during heating (low thermal conductance) to another workingfluid with a different conductance during cooling (high thermalconductance).

In yet another alternate configuration, the gas feed through 116 isdivided into two or more passageways with one end of each passage wayfluidly connected to a separate pressure regulator and source of gas,and the other end of each passage way fluidly connected to differentsections of the gap recess 111, where the different sections of the gaprecess 111 are separated by membrane 113. In this configuration, eachsection of the gap recess 111 can have a different thermal conductance,thereby allowing spatially variable heating and cooling.

FIGS. 7 and 8 depict an alternative embodiment of the gap assembly 104′,where the gap body 184 is provided with an alternative configuration.FIG. 7 is a plan view of an alternate embodiment of the gap assembly104′ that includes a first step section 148, a second step section 150,and a third step section 152. FIG. 8 is cross-sectional view taken alongline VIII-VIII of the alternate embodiment of the gap assembly 104′ thatincludes the gap section 111, the vacuum feed 138, and conduit 142. Thefirst step section 148, the second step section 150, and the third stepsection 152 are annular portions of floor. The step sections arearranged such that the height (or distance between the upper surface ofthe step section and the top of the gap assembly 104′) of the gap recess111 varies spatially from section to section. By varying the gap recessheight, the thermal conductance of the gap can also be varied.

In operation, this embodiment operates exactly the same as the firstembodiment, except that the presence of first step section 148, secondstep section 150, and third step section 152 causes a spatial variationin the conductance of the gap according to the height of the gap recess111 above each step. It should be clear to those skilled in the art thatthe annular arrangement of steps is but one possible configuration ofstep heights, and that many other arrangements are possible. The stepheights can vary in ways other than as shown in FIG. 8. For example, itmay be advantageous to reverse the sequence of step heights from low tohigh to a sequence of high to low. Moreover, the gap thickness in FIG. 8is depicted as being stepped, but it may alternatively be smoothlyvarying, for example, by making the floor a convex and/or concavesurface.

It should be further noted that an additional alternative embodiment ofthe present invention is configured such that the locations of theheating 102 and the cooling assembly 106 are switched. In thisconfiguration the cooling assembly supports the substrate 108 and theheating assembly is located below the gap assembly. Thus, the coolingassembly may be an electrostatic chuck manufactured by Tokyo ElectronLimited, or the one disclosed in U.S. Pat. No. 5,310,453 entitled“Plasma process method using an electrostatic chuck” and assigned toTokyo Electron Yamanashi Limited (Fukasawa et al.), or U.S. PatentApplication Ser. No. 60/156,595, filed Sep. 29, 1999 and InternationalApplication No. PCT/US00/25503, filed Sep. 18, 2000. U.S. Pat. No.______, incorporated herein by reference. In such a configuration, thecooling channel feed 120 and/or the cooling channel return 122 of FIG. 1are utilized to carry the heater wires 194 from the power supply 157 tothe electrical resistive element 110. Additionally, the conduit 142 ofFIG. 1 is split or sectioned into or provided as two parallel tubes,where one tube acts as the cooling channel feed and the other tube actsas the cooling channel return, thereby supplying working fluid from thecoolant fluid supply and pump 173 to the coolant channel 112, and back.Such a configuration will be readily apparent to one of ordinary skillin the art based upon the above disclosure of the various embodiments ofthe rapid thermal processing assembly 100.

FIG. 9 is a flow chart setting forth a first method of operation thatcan be used with the first embodiment of the rapid thermal processingassembly 100. In step 200, the substrate 108 is loaded onto thesusceptor. The processing assembly is preferably configured toaccommodate the passage of three lift pins (not shown) through theassembly in order to (1) lower the wafer to make contact with thesusceptor during loading and (2) raise the wafer above the susceptorduring unloading. The processing environment is established and thewafer is exposed to the environment (e.g., gas, pressure, etc.). Duringstep 210 the gap recess 111 is evacuated until a prescribed pressure hasbeen reached, or alternatively for a prescribed amount of time. In fact,step 210 can be accomplished during step 200.

In step 220, the substrate 108 is heated to a desired temperature by thecontroller 156 sending a signal to the power supply 157 to deliverelectrical energy to the electrical resistive elements 110 via heaterwires 194. With the substrate 108 on the heating assembly 102 of therapid thermal processing assembly 100, a command from the controller 156causes the second valve 130 to be opened to vacuum pump 126, and thefirst valve 128 to be opened. As a result, any residual gas in thevacuum feed 138 and in the gap recess 111 is pumped out.

In step 230, the controller 156 closes the first valve 128, sets thesecond valve 130 to the working fluid setting, and sets the pressureregulator 134 to allow a predetermined flow rate of working fluid fromthe helium gas supply 136. The pressure regulator 134 will set thepressure of the working fluid delivered to the gap recess 111. In analternate embodiment, high pressure (i.e. atmospheric pressure) workingfluid can be caused to flow through an inlet to the gap recess andexhaust the working fluid through an outlet in order toconductively-convectively cool the wafer or backside of the heatingplate or heating assembly.

In step 240, the process status is queried to determine whether or notthe process is over. If the process is determined as not being over,then the process loops back to step 230 and the working fluid continuesto flow or maintain a specified gas pressure in the gap. If the processis determined to be over, then the process ends in step 250.

The apparatus of the present invention is capable of more complexprocesses than simply heating a wafer. FIG. 10 is a flow chart showing asecond method of operation that allows for different wafer temperaturesin each of multiple process steps. The method extends the first methodof operation, and includes the modifications as discussed below.

In step 335, the settings for the gas pressure regulator are read frommemory in the controller 156, and the controller 156 sends a command tothe pressure regulator 134 to set the working fluid flow from helium gassupply to the appropriate level to achieve a desired working fluidpressure. If the recipe in the memory in the controller 156 alsoindicates a change in power to be applied to the electrical heatingelements 110, then the controller 156 sends an instruction to the powersupply 157, which subsequently adjusts the amount of electrical powerdelivered to the electrical resistance heaters 110 via heater wires 194.Furthermore, if need be (as indicated by the process recipe), thecontroller 156 can turn the pressure regulator 134 off, turn the secondvalve 130 to the vacuum pump 126, and open up the first valve 128.

Later, if step 240 determines that the process is not over, then theprocess proceeds to a determination of whether it is time to change theprocess in step 345. In step 345, if it is determined to be time tochange the process, then the new process settings are loaded into thememory and the process loops back to step 335 and the process proceedsfrom step 335 as described above. Once the process reaches step 250, theprocess ends.

In the second method of operation, once a wafer is loaded onto the rapidthermal processing assembly 100, the controller 156 accesses a processrecipe in the memory. The recipe includes a sequence of steps asdescribed above. For each step, there is a configuration for the firstvalve 128, the second valve 130, the pressure regulator 134, the vacuumpump 126, and the power supply 157. Further associated with each step isa time during which a given set of valve settings, power supplysettings, etc. are applied. In operation, the controller 156 stepssequentially through each step in turn, executing the processinstructions in each step as indicated by the recipe.

It should be clear to those skilled in the art that variations in thesequence of heating and cooling, as well as variations in the valvesettings and gas flow conditions are possible. Such variations can beused advantageously to control the rate at which wafers or othersubstrates reach desired process temperatures.

Generally speaking, the method for reducing thermal burden on a waferduring processing of the present invention includes the steps of heatingthe wafer to a predetermined temperature when needed using a heatingassembly, cooling the wafer to the predetermined temperature when neededusing a cooling assembly located such that a thermal conductance regionis provided between the heating assembly and the cooling assembly, andadjusting a thermal conductance of the thermal conductance region to aidin heating and cooling of the wafer. Preferably, the controller 156controls the process, and adjusts the temperature of the substrate 108as described above to achieve the desired temperature for the substrate108.

The method preferably provides for the step of heating the wafer byutilizing an electrical resistive element 110 attached to a heating body196 adapted to support the substrate 108. The step of cooling the waferpreferably includes feeding a cooling fluid along a fluid path, such ascoolant channel 112, within the cooling assembly 106.

The step of adjusting the thermal conductance of the thermal conductanceregion includes the steps of providing a body within the thermalconductance region, where the body has a recess configured to define atleast a portion of a chamber configured to receive a working fluid, andadjusting a pressure or density of working fluid present within thechamber, for example, using the first embodiment of the apparatus of thepresent invention as depicted in FIGS. 1-8. The step of adjusting thepressure or density of working fluid present within the chamberpreferably includes the step of evacuating the working fluid from thechamber during the step of heating the wafer and injecting the workingfluid within the chamber during the step of cooling the wafer.Alternatively, the step of adjusting the pressure or density of theworking fluid present within the chamber includes the step of injectinga first working fluid within the chamber during the step of heating thewafer and injecting a second working fluid within the chamber during thestep of cooling the wafer. The step of providing a body within thethermal conductance region preferably includes the step of providing amembrane within the recess, the membrane defining separate sectionswithin the chamber. Furthermore, the step of adjusting a pressure ordensity of working fluid present within the chamber preferably includesthe step of providing a separate working fluid within each of theseparate sections of the chamber. Alternatively, the step of providing abody within the thermal conductance region includes providing a bodywith a recess that has a side wall and a base, the side wall abuttingthe heating assembly such that the heating assembly, the side wall, andthe base define the chamber, where the base is spaced apart from theheating assembly by a gap distance, and the base is configured such thatthe gap distance varies over the base, such as depicted in FIGS. 7 and8.

It should be noted that the structure of the embodiments of the presentinvention set forth herein have the potential for vacuum and gas leaks.However, the implementation of a good configuration and careful plumbingwill minimize the risk of leaks. Additionally, the vacuum integrity ofparts that are bonded together is important to the effectiveimplementation of the present invention. However, careful attention tosuch issues during assembly will minimize this potential problem.

One operability issue for the present invention is difficulty incontrolling the actual height of gap recess 111 if it is less thanapproximately 25 μm. This condition would affect the repeatability oftemperature control. However, in most applications, the height of gaprecess 111 is likely to be much greater than 25 μm.

It should be noted that the exemplary embodiments depicted and describedherein set forth the preferred embodiments of the present invention, andare not meant to limit the scope of the claims hereto in any way.Numerous modifications and variations of the present invention arepossible in light of the above teachings. It is therefore to beunderstood that, within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described herein.

1-5. (canceled)
 6. A thermal processing apparatus comprising: a heatingassembly adapted to support a wafer for processing; a cooling assemblylocated such that a thermal conductance region is provided between saidheating assembly and said cooling assembly; and a device configured toadjust a thermal conductance of said thermal conductance region; whereinsaid device comprises a body having a recess configured to define atleast a portion of a chamber configured to receive a working fluid, anda fluid injection system configured to inject a working fluid withinsaid chamber, and a control system configured to control said fluidinjection system to achieve at least one of a predetermined density anda predetermined pressure of working fluid within said chamber, and saiddevice includes a pressure regulator, said control system beingconfigured to control said pressure regulator. 7-17. (canceled)
 18. Athermal processing apparatus comprising: a heating assembly adapted tosupport a wafer for processing; a cooling assembly located such that athermal conductance region is provided between said heating assembly andsaid cooling assembly; and a device configured to adjust a thermalconductance of said thermal conductance region, wherein at least one ofsaid heating assembly and said cooling assembly comprises at least oneof quartz, alumina, sapphire, aluminum, carbon, silicon carbide, andsilicon nitride.
 19. A thermal processing apparatus comprising: aheating assembly adapted to support a wafer for processing: a coolingassembly located such that a thermal conductance region is providedbetween said heating assembly and said cooling assembly; and a deviceconfigured to adjust a thermal conductance of said thermal conductanceregion, wherein said heating assembly comprises aluminum.
 20. (canceled)21. A thermal processing apparatus comprising: a heating assemblyadapted to support a wafer for processing; a cooling assembly locatedsuch that a thermal conductance region is provided between said heatingassembly and said cooling assembly; and means for adjusting a thermalconductance of said thermal conductance region, wherein said means foradjusting the thermal conductance of said thermal conductance regioncomprises a body having a recess configured to define at least a portionof a chamber configured to receive a working fluid, and means foradjusting at least one of a pressure and a density of working fluidpresent within said chamber.
 22. A thermal processing apparatuscomprising: a heating assembly adapted to support a wafer forprocessing; a cooling assembly located such that a thermal conductanceregion is provided between said heating assembly and said coolingassembly; and means for adjusting a thermal conductance of said thermalconductance region, wherein at least one of said heating assembly andsaid cooling assembly comprises at least one of quartz, alumina,sapphire, aluminum, carbon, silicon carbide, and silicon nitride. 23-26.(canceled)
 27. A thermal processing apparatus comprising: a coolingassembly adapted to support a wafer for processing; a heating assemblylocated such that a thermal conductance region is provided between saidheating assembly and said cooling assembly; and a device configured toadjust a thermal conductance of said thermal conductance region, whereinat least one of said heating assembly and said cooling assemblycomprises at least one of quartz, alumina, sapphire, aluminum, carbon,silicon carbide, and silicon nitride. 28-29. (canceled)
 30. A thermalprocessing apparatus comprising: a cooling assembly adapted to support awafer for processing; a heating assembly located such that a thermalconductance region is provided between said heating assembly and saidcooling assembly; and means for adjusting a thermal conductance of saidthermal conductance region, wherein said means for adjusting the thermalconductance of said thermal conductance region comprises a body having arecess configured to define at least a portion of a chamber configuredto receive a working fluid, and means for adjusting at least one of apressure and a density of working fluid present within said chamber.31-42. (canceled)